The invention concerns a method for ratio control/rotational speed control for a continuously variable automatic transmission of a motor vehicle.
A continuously variable automatic transmission usually consists of a starting unit, a forward-reverse drive unit, an intermediate shaft, a differential, hydraulic and electronic devices and a variator. The variator usually comprises a primary and a secondary variator. In a variator according to the belt-drive principle, the variator is customarily designed with beveled pulleys disposed in pairs and provided with a torque-transmitting belt-drive element which rotates between the two pairs of beveled pulleys. In such a transmission, the actual ratio is defined by the running radius of the belt-drive element which, in turn, is a function of the axial position of the beveled pulleys.
According to the prior art, in the control of continuously variable transmissions, the primary rotational speed of the variator or the engine rotational speed is, as a rule, selected as a control variable for adjusting the operating point predetermined by a superimposed driving strategy.
Customarily, control loop structures such as described in the Applicant""s patent No. DE 196 06 311 A1 are used. Such control loop structures combine a physical-mathematical pattern-based linearization of the control system with a linear PID controller, by means of a correcting member (inverse pattern).
According to the prior art the behavior of the hydraulic system is taken into account empirically and, therefore incompletely, within the scope of a very simple mechanical adjustment pattern. This results in a sequence behavior of the control loop that is not optimal, whereby the stationary precision, and the basic dynamics of the closed control loop are impaired.
The speed of the control hydraulics is for this reason a xe2x80x9cbottle neckxe2x80x9d in the efficiency of the whole control, since it sharply decreases at low temperatures (particularly below 200xc2x0 C.) when case said pattern-based temperature has not been explicitly taken into account.
The problem on which this invention is based is, on the basis of the prior art cited, to take temperature dependently and dynamically into account in the hydraulics control in order to improve the basic behavior of the control loop, in a manner such that the stationary precision and the basic dynamics of the control loop are improved during the traction/push load changes.
Another object of the invention is to substantially increase the speed of the control hydraulics and to improve the on and off adjustment in LOW and OD (overdrive).
Accordingly, a state-assessment is proposed to assess an interference force (variable FL) from the adjustment pattern of the variator. According to the invention, this is done by introducing an interference-variable observer. The interference force results from principle-conditioned characteristic line errors, other stationary and dynamic pattern errors, and deficiencies in the easily selected mechanical adjustment pattern. The interference force therefore reproduces all inaccuracies of the mathematical pattern relative to the real system.
Due to the complex adjustment behavior of the variator, a purely pattern-based compensation of errors is possible only by higher order patterns which are purposefully eliminated the scope of the invention.
According to the invention, the adjustment pattern of the variator and the temperature-dependent pressure dynamics for both variator pulleys are taken into account in the controller pattern.
It is assumed that the influence of temperature acts essentially upon the actuator dynamics or adjustment dynamics.
According to the invention, controller adjustment of the corresponding non-linear compensation controller can be automatically adjusted according to current methods, since the entire transmission function is time variant and the time variation consists only of the temperature portions of the hydraulics which are assumed to be quasi-stationary (the oil temperature of the transmission changes slowly compared to the total dynamics.)
The method, according to the invention, is based on a non-linear compensation method according to the principle of exact linearization.
According to the invention, this means that the controller pattern of the hydraulics can be preferred as a block over the inverse route pattern and the route pattern so that a simple transmission function results.
The whole controller design, including the hydraulics routes is possible according to a main feature of the present invention by the compensation control principle, as a temperature-dependent linear control loop which contains only the parameters of controller amplification, attenuation, and time constants of the hydraulics, which on both sides are temperature dependent.
The mechanical stop can be detected by the observer. The system limits LOW and OD are thus specifically detectable relative to the vehicle, by the observer. Other route properties (e.g. variator attenuation) are, likewise, adjustable or also detectable.